add a `hydrator` param that allows adding/modifying file attributes

[manuhabitela]

This is in relation to my question in #56.

Adding a function allowing full control of how data is set on the syntheticFile allows me to handle React Helmet in static-only mode.

Here is a gist to show how I managed to get what I want.

[yeojz]

@Leimi Thank you so much for sending in a PR!!.. Looks great. 👍

2 suggestions:

• Rename this to postRender instead of hydrator. I think it describes the placement within the flow better. What do you think?
• Possible to add in an example in README for a sample "hydrator" for helmet?

Thanks again!!

[manuhabitela]

Oh I forgot to link the gist I was talking about to show how I made everything work, here it is https://gist.github.com/Leimi/b62975a28b202fb6919fa7feb7688f5b.

About the postRender renaming, if you want, but I'm not sure. I'm not that fond of "hydrator" myself but I choosed it because it implied the function was supposed to return some attributes to put in an object. postRender doesn't give that information at all...postRenderHydrator? :p

[manuhabitela]

I added some more info in the README, what do you think?

Waiting on your final input on the naming to change things if needed. Thanks!

[yeojz]

Noted on that point. Personally, I was hesitant about hydrator partly also because the newer ReactDOM also has a hydrate function which may be confusing.

It is a bit of a mouthful, but let's go with your suggestion of postRenderHydrator. :+1:

Will merge after that change. Thanks!

[manuhabitela]

Okay thanks, I updated the branch.

[manuhabitela]

Thanks for merging!